There are many known prior art arrangements for limiting the charging air pressure of an internal combustion engine supplied with a turbocharger, especially in aircraft applications. The basic concern with respect to aircraft applications is maintaining a constant intake manifold pressure at all altitudes of flight in order to insure continuous maximum operation of the aircraft engine. In aircraft applications, it is important to maintain a constant manifold pressure as a function of either manifold temperature, engine oil pressure and, of course, the ambient surrounding conditions in order to maintain a safe maximum output of the engine while the aircraft is operating. In addition, aircraft systems are designed such that there is a manual override of the turbochargers in order to permit a pilot to exercise his discretion with regard to its operation. As a result, aircraft systems are designed with a multiplicity of levers in order to enable manual override of the various regulating devices.
U.S. Pat. No. 2,776,720, issued Jan. 8, 1957; U.S. Pat. No. 2,833,355 issued May 6, 1958; and U.S. Pat. No. 2,901,885 issued Sept. 1, 1959 to F. C. Reggio, are typical examples of the aforementioned type of aircraft engine controlled devices which are utilized to maintain constant manifold pressure as a function of other engine and ambient parameters. U.S. Pat. No. 2,710,522 issued June 14, 1955 to Jorgensen and U.S. Pat. No. 2,540,916 disclose turbochargers for aircraft applications wherein an electrical portion and controls systems are utilized sequentially for controlling throttle position and compressor speed.
Miller, in U.S. Pat. No. 3,015,934 issued Jan. 9, 1962, teaches the control of the inlet or the exhaust valve opening as a function of the load on the engine. Miller accomplishes this by delaying either the inlet or the exhaust valve closing in one embodiment so as to allow the turbocharger to pick up speed at full load and maintain constant air/fuel ratios to the engine.
Powell et al, in U.S. Pat. No. 3,386,427 issued June 4, 1968, is concerned with a fuel system wherein the system meters the fuel delivered to the turbocharger through the use of an engine driven fuel pump and a regulating device to regulate the delivery of fuel as a function of the throttle position. Manual controls are used to override the metering system in order to provide a throttle control for economy cruising or idle cut-off by the pilot. Powell also teaches a device for controlling the turbocharger speed which is responsive to the discharge pressure of the throttle with an atmospheric pressure control override at the critical altitude.
U.S. Pat. No. 3,487,634 to May et al, issued Jan. 6, 1970, discloses an internal combustion engine with a turbocharger and a fuel control system. This system, when matched with a transmission having a relatively small number of speed change ratios therein, provides enhanced vehicle performance for the generation of substantially constant horsepower output of the engine throughout the normal operating range of the engine.
Nettel, in U.S. Pat. No. 2,620,621 issued Dec. 9, 1952, teaches a diesel engine having a control auxillary burner means to supplement the exhaust gas feed to the turbocharger so that the engine is able to deliver greater crankshaft torque at lower speeds than at higher speeds. At the same time, the device delivers a constant power output within a wide speed range without the use of speed changing devices.
The patent to Udale, U.S. Pat. No. 2,578,028 issued Dec. 11, 1951, discloses a two-stage turbocharger to obtain short period increases in power without exceeding the temperature limits of the turbine.
Lloyd, in U.S. Pat. No. 4,005,579 issued Feb. 1, 1977, is directed to the problem of diverting exhaust flow at the maximum engine speed and thereby avoids overdrive of the turbine and compressor. Thus, Llyod avoids excessive manifold pressure at part-throttle engine conditions.
The fuel control system taught by Schueler et al, in U.S. Pat. No. 3,981,285 issued Sept. 21, 1976, provides an excess fuel quantity during engine acceleration through the use of manifold pressure actuated control units. The control units consist of diaphram valves wherein one valve is throttled. This results in a net differential control force tending to increase the fuel supply to the injection nozzles of the engine injection system while the manifold pressure is rising.
None of the above cited references, however, is directed to the problem of providing a fuel cut-off to the internal combustion engine for a given overboost pressure situation.
The patent to Drayer, U.S. Pat. No. 3,049,865 issued Aug. 21, 1962, is directed to the problem of overcoming the time lag required by the compressor of the turbocharger to supercharge the air. Drayer provides a control system which includes a bypass conduit extending between the compressor inlet conduit and the compressor outlet conduit. In addition, a throttle valve means is suitably disposed in the bypass conduit and compressor inlet conduit and operatively connected to open and close together. This valve mechanism allows the compressor to run at full speed at all times and during part throttle operation, a portion of the air is diverted through this valve mechanism. When supercharging is required, the high rotational speed of the compressor permits the compressor to supercharge the air without the usual time lag which is experienced.
The only other known prior art device having a fuel cut-off valve actuated by an overspeed governor is the patent to Poole, U.S. Pat. No. 2,609,656 issued Sept. 9, 1952. Poole is directed to a gas turbine power plant with an arrangment for cutting of the fuel supply to the gas turbine burner in the event of the turbine overspeeding. Another feature of Poole's device is that it cuts off all fuel flow to the power plant when the turbine exceeds a predetermined speed.
In summary, therefore, none of the above identified prior art devices provides a mechanism for controlling fuel flow to an internal combustion engine having a turbocharger such that fuel flow rate to the engine increases in response to increases in intake manifold pressure up to a predetermined pressure level and such that the fuel flow to the engine is decreased to a idle cut-off fuel flow rate when the intake manifold pressure is greater than the predetermined pressure level so as to protect the reciprocating engine from overpressurization of the engine by the turbocharger.